Track circuit responsive to varying train-shunt



F. X. REES Dec. 17, 1957 TRACK cmcun' RESPONSIVE T0 VARYING TRAIN-SHUNT Filed March 5, 1954 FIG-.1.

3 Sheets-Sheet 1 TRACK RAILS SWITCH AND/0R SIGNAL CONTROL R m 8 NEW mE A R X F W7 .2

m w .m mm M m mm HIS ATTORNEY Dec. 17, 1957 F. x. REES 2,8 7

TRACK CIRCUIT RESPONSIVE TO VARYING TRAIN-SHUNT Filed March 3, 1954 3 Sheets-Sheet 2 FIG 2 2 I 2 k 3 /TF-QACK RAILS {3- TR 4 WW I I B LR SWITCH 22 AND/OR- SIGNAL CONTROL FIGuS,

SWITCH l AND/0R W $2323. WENT BY F. X. REES i ATTORNEY F. x. REES 2,817,010

TRACK CIRCUIT RESPONSIVE TO VARYING TRAIN-SHUNT Dec. 17, 1957 5 Sheets-Sheet 3 Filed March 3, 1954 FIG.4.

TRACK RAILS 3 4 I... 4 4 L CO T/ I NT WN ASw INVENTOR. F. x. REES 7MW section through its own front contact.

TRACK CIRCUIT RESPBNSIVE TO'VARYING TRAIN-SHUNT Frank X. Rees, Chili, N. Y., assignor to General Railway Signal Company, Rochester, N.

Application March 3, 1954, Serial No. 413,818 14 Claims. (Cl. 246-41)- This invention relates to direct current track circuits for railroadsaand more'particularly pertains tomeans for increasing the reliability of such track circuits in their response to train-shunts.

In: the. usual direct current track circuit, a source of direct current is connected across thetrack' rails at' one end of" a track section in series with a limiting resistor; and a track relay of suitable resistance is connected across the track rails at the other end of'the track section. The values of relay and limiting resistances involved are selected in accordance with the range of variation in the ballast conditions for the particular track section assuming a particular maximum permissible value of a. trainshunt resistance. Normally the track relayjis energized; but, when a train .enters the track section and shunts the rails, the current is, reduced in the relay to a low value causing it to drop away.

Although the conventional track circuit above described hasbeen found to be most reliable and effective forthe operation of trains in the past, at the present time, the trains are being operated at such high speeds. and some trains are so short and light weight as. to produce circumstances where such conventional track circuits may fail; In f'act,,many railroads are employing, single diesel-powered passenger units which are relatively light and have a minimum number of axles for shunting a track circuit. In addition, the sanding of the rails in connection with relatively short trains. during a braking operation sometimes makes it almost impossible for the train tobe effective as a train-shunt.

In view of the above and other important. considerations, it is one purpose of the. present invention to provide a track circuit organization which is quick in its response to the entrance of a train, and which is effective duringthe passage of a train to maintain an indication of the presence of the-train in spite of varying train-shunt values.

Another purpose ofthe presentinvention is to. provide a track circuit organization which. is distinctively responsive to the initial entrances and exits of cars. as well as to thevarying values of train-shunt during the passage of a train through the section, which organization is arranged to be inherently self-checking.

Generallyspeaking, and without making any attempt to define the exact nature of the invention, it is proposed. to provide a track circuit with a stick circuit arrangement which is released whena ca-r ortrain enters. the associated track section and is. restored or picked up when the track section becomes unoccupied.

In one form, the stick circuit arrangement is provided by connecting the track relay to the rails of the track In another form, the stick circuit arrangement is provided by using an auxiliary stick relay associated with the track relay. In both forms, animpulse transformer is connected across the track rails in such a way thatcurrent changes in the track circuit produce impulses which are supplied tent O 2,3173% Patented Dec. 17, 1957 ice through a rectifier unit to a sensitive impulse relay means. In the first mentioned form, the shunting of the track relay when the section becomes occupied causes the release of the track relay stick circuit arrangement; and the actuation of'the sensitive impulse relay means when the section becomes unoccupied provides a pick-up circuit for the track relay. In the second mentioned form, the sensitive" impulse relay means opens the stick circuit for the auxiliary stick relay when the section becomes occupied; and this same sensitive relay means also provides a'pick-up circuit'for the auxiliary relay when the section becomes unoccupied. Also, in both forms the stick circuit arrangement and the sensitive impulse relay means govern the control of associated signaling circuits so as to provide a quick detection of the occupancy of the associated track section.

In addition, all forms of this organization provide that changes in the train-shunt values as a train passes through a section, either due to the condition of the track rails, the sanding thereof, or other conditions, will cause variations in the current in the track circuit in such a way as to cause the response of the impulse relay means. Thus, should the train-shunt become sufficiently ineffective as to allow the energization of the regular track relay, the changes would act on the impulse relay means and hold the signals at stop in spite of the undesired response of the track relay. In other words, continuously recurring losses of train-shunt are just as effective to hold the signals at stop as a steady value proper train-shunt.

Since a track relay once released'cannot be picked up unless the impulse responsive relay means operates properlyupon the exit of a train, thereis a recurring check upon the operativeness of the impulse responsive means. In other'words, a failure in the impulse responsive means is self=betraying, which is a prerequisite of railway signaling systems;

Other objects, purposes and characteristic features. of

the present invention will in part be obvious from the accompanying drawings and will in part be more specifically described hereinafter;

In describing'the invention in detail, reference will be made to the accompanyingdrawings, in which like referencecharacters designate corresponding parts throughout the several views, and in which:

Fig, 1 is a diagrammatic view of a track section and associated apparatus to constitute one form of track circuit embodying the present invention, which form is moreparticularly applicable to short track circuits;

Fig. 1A is a modification of Fig. l to provide selective control of the impulse responsive apparatus;

Fig. 2 is a diagrammatic view of a track section and associated apparatus to constitute a second form of track circuit embodying the present invention, which form is more particularly adapted for use in connection with relatively long track circuits;

Fig. 3 is a diagrammatic view of a track section and associated apparatus to constitute a third form of track circuit embodying the present invention, which form is particularly adapted to track circuits that are relatively long and in which the impulse responsive apparatus is effective to release the track relay as well as to pick it up; and

Fig. 4 is a diagrammatic view of a track section and associated apparatus to constitute a fourth form of track circuit embodying the present invention, which form is particularly adapted to track circuits that are relatively long and in which the track relay is connected directly across the track rails with the impulse responsive apparatus connected in multiple therewith and effective to rel'easethe track relay as well as pick it up.

For the purpose of simplifying the illustration and facilitating in the explanation, the various parts and circuits constituting the embodiment of the invention have been shown diagrammatically and certain conventional illustrations have been employed, the drawings having been made more with the purpose of making it easy to understand the principles and mode of operation, than with the idea of illustrating the specific construction and arrangement of parts that would be employed in practice. Thus, the various relays and their contacts are illustrated in a conventional manner.

With reference to Fig. l, a track section having rails 2 is shown as being separated from adjoining sections by suitable insulated joints 3. At the right-hand end of this track section is shown a transformer TF having primary winding 4 and secondary winding 5. This transformer TF has its primary winding 4 connected in series with a battery B and a limiting resistor LR across the two track rails. The secondary winding 5 of the transformer TF is connected through a full-wave rectifier RE to the windings of an impulse relay IR which is a very sensitive relay and responds to very small values of current.

The transformer TF is suitably designed to have its primary winding 4 of very low ohmic resistance so that its inclusion in series with the battery will not unduly decrease the interrail potential nor cause any substantial increase in interrail potential should it become short-circuited. In addition, this transformer TF may be of the closed magnetic circuit type which is more efiicient with regard to the transfer of energy. However, if it is desired to increase the rate of transfer of energy, this transformer TF may be of the open magnetic circuit type.

At the other end of the track section, a track relay TR is connected across the track rails through its own front contact 6 to constitute a stick circuit. In multiple with the contact 6, two wires 7 and 8 extend to the other end of the track circuit so that they can be connected through front contact 9 of relay IR, when this relay is picked up, to complete a pick-up circuit for the track relay TR.

Also associated with the track relay TR is a repeater relay TRP which is controlled through front contact 10 of relay TR, battery 11, wires 12 and 13, and back contact 14 of relay IR.

Since the conditions of track relay TR and the impulse relay IR are combined in the track repeating relay TRP,

the contacts of this repeating relay TRP, such as contact 15, may be used for governing any control of the switch and/or signals which may be associated with this track section. In this connection, it should be recognized that this track section may include one or more track switches, and there may be electric switch locks,-power operated switch machines, and the like, which are associated with these track switches and which, in accordance with the usual practices of railway signalling, would be governed by a track relay to prevent their improper operation while the track section is occupied. Likewise, a signal may be provided for governing traflic over the track section; and it is usual practice to select such signal through contacts of the track relays for the sections over which it governs tralfic. It is to be understood that all such control is assumed to be provided in accordance with the usual practices which has been indicated as being eflfected by contact 15 of the track repeating relay TRP. The details of such features have not been shown because they are well understood in the art and may be assumed to be conventional.

When considering the operation of a track circuit there are at least two conditions which should be considered. In the first place, there is a situation Where the wheels and axles of a train constituting a train-shunt are effective to provide substantially a short circuit across-the track rails. Such a train-shunt is usually present when the track rails and the train wheels are in good condition. In the second place, there are conditions where the rails may be .rusty or have an oil film, a coating of sand or the like so that the entrance of a train with its shunting wheels and axles is not effective to produce the substantial short circuit, but is only elfective to somewhat reduce the interrail potential. When a train-shunt of this character is present, it has been found that it continuously varies as the train passes through the track section. In some instances, these changes may be of such a character as would be provided by the intermittent application of a short circuit across the rails.

No attempt has been made to graph these changes because they are of random character and they have dilferent shapes dependent upon where the interrail potential is taken and dependent upon the inductive and resistive character of the track relay as well as upon whether there is an external limiting resistor in series with the track relay leads. In any event, under poor track circuit conditions of this kind, the variation in the train-shunt characteristics results in variations in the current value supplied by the track battery source, and also variations in the interrail potential supplied to the track relay.

It will be assumed that the track circuit design is proper in accordance with the best practice for responding to train-shunts, and that the track circuit, regardless of its particular design characteristics, will have varying interrail potentials during the passage of a train under poor train-shunt conditions just mentioned.

For convenience in the present discussion, let us now consider that a train providing a relatively good trainshunt enters the track section of Fig. 1. When this trainshunt is applied across the track rails, current from the battery source B is shunted away from the track relay TR and the interrail potential at the track relay end is reduced to a very low value. For the best train-shunts this value of interrail potential is too low to read on the conventional meter. Since the track relay TR is inductive in its structure, it tends to be slightly slow in its releasing, because the energy stored in its inductance must discharge through the rails and the train-shunt. As soon as this discharge has taken place to the point of drop away for the relay, its contacts are released, opening contacts 6 and 10.

The train-shunt is of relatively low resistance which causes an increase in the current flow through the track rails from the battery B at the other end of the track section, but the rise of this current is retarded both by the inductance of the track rails and by the inductance of the transformer TF. This rise in current through the primary winding 4 of the transformer TF causes an impulse of energy in the secondary winding 5 of this transformer. This impulse is applied to the impulse relay IR through .the rectifier RE causing the contacts of this relay to be quickly picked up. The opening of back contact 14 of relay IR usually drops the relay TRP before the contact 10 of the track relay TR opens. This opens the control of the switch and/or signal apparatus very quickly by the opening of front contact 15 of the track relay repeater TRP. In this way, this track circuit organization is very quick in its response to the entrance of a train.

The presence of the good train-shunt across the track rails has reduced the voltage across the relay TR so that it remains dropped away in spite of the fact that the front contact 9 of relay IR is temporarily closed immediately following the entrance of the train. In this connection, the transformer 'DF has considerable stored energy in it which supplies a substantial pulse of current to relay IR. Also,the full-wave rectifier RE connected across the wind ings of relay IR tends to make this relay IR slow to drop away. In other words, the entrance of the train releases the track relay TR and also causes the relay IR to be quickly picked up to close contact 9 for a short interval of time. However, when the conditions have stabilized themselves after the entrance of thetrain, therelay IR drops away and the relay TR remains dropped away..

Assuming that the train-shunt is of a proper value to maintain the track relay TR dropped away, the current rough the primarywinding of thetransfomner' 1 F remains. fairly steady andno. impulses are. supplied to: the impulse relay IR as the. train passes throughv thesection. But when the train leaves the track section, the trainshunt is of course rather abruptly removed so that the relatively large current through the primary winding 4 is reduced to a normal value. This abrupt change in current causes. another impulse of energy to be supplied to the relay IR causing it to pick up its contacts. The closureof contact 9 completes the. pick-up circuit for the track relay TR so. that it canrespond to the normal value of energy supplied to the track rails..

It should be noted that the heavy current which flows through the primary winding of the transformer TF while the train-shunt is present stores considerable energy, so that when. the train-shunt is removed this energy in efiect provides a voltage which is additive to thevoltage of the battery B and in this way increases temporarily the voltage across the track rails. This has a tendency tQ-increase the rate at which the current rises in the .track relay TR so that it picks up fairly quickly. In any event,.the impulse energy which is supplied to relay IR. together with its. releasing characteristics, as above mentioned, causes the contact 9 of this relay to remain closed sufliciently long for the track relay TR to respond to the normal energization of the track circuit.

It is. obvious that the track repeating relay T-RP is. not picked up until the track relay TR has been picked. up and the impulse relay IR has assumed a. normalreleased position. This assures that the switch and/ or signaldevices are not released for operation until the. track section isunoccupied and restored to normal conditions.

From the above description, it will be noted that the restoration of. the normal conditions require that the impulse. relay IR respond, i. e. track relay TR cannotbe picked up unless the impulse relay IR closes front contact 9. Thus, should there be a short circuit in winding 4, an open circuit in winding 5 or a break in the connections to the impulse relay IR or in its winding, the track relay TR would remain dropped away. This would cause the switch and/ or signal control to remain. locked while no trainwas present, which condition would be brought to the attention of train crews and/ or maintainers in .such a way that it would be reported and the. difliculty remedied. In other words, the provision of this apparatus for quickly responding to train-shunts is fully checked.

This form of the invention shown in Fig. 1 is particularly useful in connection with short track circuits. as it is obvious that the wires 7 and 8 together with. contact 9 should preferably be of relatively low resistance since the interrail potentials found in track circuits are relatively low. For example, the track circuit of Fig, 1 is very useful in connection. with car retarder yards where the track relay and the track battery, impulse transformer, rectifier and impulse relay may all be housed in the same relay case. However, it should be understood that this form of the invention may be used with longer track circuits employing line wires if desired.

When the invention of Fig. 1 is used in connection with the detector track circuits of car retarder yards, itis desirable not only to provide quick responseto a shunt but also to have a quick release of the. detecting apparatus when a car or train leaves the track section. Asabove mentioned, the impulse relay IR may; be maintained picked up for a substantial interval of time due to. the inductance of the transformer TF and the short circuiting characteristicsof the rectifier RE with respect tothe, windings of relay IR.

Taking these factors-into. consideration, the. form of Fig. 1A modifies the. form of Fig. 1 in such away as to provide .a control for causing the" relay IR to be 'main .tained, picked up for a shorter interval of time when a train leaves the track section. More. specifically, the. transformer, 1TH is provided with a secondary, winding;v 1,6 which has. acenter tap connected. to, the. impulse. relay 1K. The. left-haniterminal of: this winding'16is connected. throughrectifier unit- 17 to. the other terminahof the impulse relay IR. The. right-hand terminal of winding. 16. is connected through a. variable resistor 18 and rectifier unit19 to. the leftrhand terminal oftheirnpulse relay IR. The connections to. the winding 16 and the manner in which the rectifiers 17 and 19 are poled determine. that the-impulse supplied to the impulse. relay IR upontheentranceof a car intothetrack section flows through rectifier. unit 17. On the. other hand, the impulse which flows from the winding 16. when a car leaves the track section passes. through. the rectifier unit 19 and resistor 18. Thus, the intensity ofthis impulse may be varied by. suitably setting the resistor 18. Since theleaving of the car from the track section-is rather abrupt and occurs atthe battery end of the section, this impulse is ratherl-arge and by reducing its vvaluewith aproper setting of. resistor 18,. the time during which the relay IR is maintained. picked. up. following the exitofthe car may be shortened to the desired length of time.

Let.us.now consider that a relatively poor train-shunt entersthe track section of Fig. 1 taken alone or as modified byFig. 1A.. The entrance of such a train-shunt.may or. may notbe adequate to shunt thetrack relay TR and cause. its. release, but itis effective. to. cause a sufiicient change in the track circuit current to efiect the response of. theimpulse relay IR. The immediate picking up of thisrelay. IR. opens back. contact 14 and releases the. repeater relayTRP to. open contact 15 and properly govern the. switch and/ or signal controls. During the movement of this train through the. track section, this relatively poor train-shuntcondition, which may be due. to various causes, acts to intermittently vary the current supply from the track battery B. In some cases, the variations arev such that a graphic view of them would make it appear that the train-shunt was a good shunt but was repeatedly interrupted in its. effect; and inother instances. it would appear that there was a very poor train-shunt effect witha repeate application of a proper train-shunt. In either case andin other intermediate conditions, there is such a recurring, series. of changes in the track circuit current from the battery Bthat the transformer TF causes pulses of opposite polarities to be. supplied through the rectifier RE to. the impulse relay IR. It is, of course, understood thatthe rise. and fall of direct current in the primary winding 4 causes pulses of opposite polarity in the secondary winding 5. These pulses of opposite polarity are properly rectified and supplied to the relay I-R. The recurrence of the pulses of course causes the actuation of the relay IR and it maintains its back contact 14 steadily open to deenergize the repeating relay TRP.

From the above description, it will then. be apparent that under the. poor train-shunt conditions, the response of the impulse relay IR to continuously. varyingtrack circuit current is effective to properly lock the switches andhold the signals at stop regardless of whether or not they track relay- TR is. actually dropped away. Since the passage. of'trains having a good train-shunt causes. the system to be self checking. with respect to the impulse responsive apparatus, it is apparent that the impulse responsive apparatus may be relied upon when trains pass which only have a relatively poor train-shunt effect on the' track circuit.

From the above it will be readily seen that thetrack circuit organization of Fig. 1 alone. or taken with Fig; 1A adequately responds to both good and poor train-shunts.

Second form (Fig. 2)

Thisform of the invention employs substantially the sameapparatus as shown in Fig. 1, but it isrearranged so as to be more adaptable to long track circuits where itisuneconomical to run. line wires between the battery and relay ends of the track. section.

More specifically, the track section isshownas: having rails 2..-separated from adjoining sections by the usual insulated joints 3. ;At the right-hand end of this track section, a battery B and limiting resistance LR are connected in series across the track rails;

At the left-hand end of this track section, the transformer TF having primary winding 4 and secondary winding 5 is associated with the track relay TR and impulse 'relay IR. The primary winding 4 is connected directly across the track rails in multiple with the track relay TR which is also connected across the track rails through its own frontcontact 20. Thus; the current supplied by the battery B to the track rails of the section divides between the winding 4 and the trackrelay TRin accordance with their respective values of "ohmic *resistance, :which are preferably about equal, butthis is not a requirement for the operability of the system.

The secondary winding 5 .of the transformer TF is connected through the full wave'rectifier RE to the windings of the impulse relay IR in the same way as described for Fig. 1. This relay IR is a very sensitive relay and responds to very small values of current. The transformer TF may be of the closed magnetic circuit type which is considered the most efficient type for the transfer of .energy. However, if it is desired to have the impulse relay IR respond more quickly to current changes in the track section, this transformer TFqmay'be made of the .open magnetic circuit type.

It will be observed thatthe track relay TR is connected 'across the track rails 2 through its own front contact 20 to constitute a stick circuit organization. Thus, .once a train has entered the track section and shunted the track relay during and immediately subsequent to the initial ;response of relay IR, it cannot again be picked up until the normal energy is returned to the track relay TR and the impulse relay IR is also actuated to close its front contact 21, which occurs when the train leaves the track section. The track relay has contact 22 and the impulse relay has contact 23, which contacts jointly control the switch and/or signal devices connected with the track section. These contacts are shown in series so as to indicate that such devices are locked or prevented from operation with either the track relay TR dropped away or with the impulse relay IR picked up. This is merely a convenient way to show in a simple manner that various traffic controlling devices such as track switches, signals, electric switch locks, power operated switch machines, and the like associated with the track section are controlled in accordance with traflic conditions.

The energy normally supplied to the track section by the battery B is adjusted by properly selecting the position of the adjustable limiting resistor LR so that there is sufficient current through the track relay TR when no train is present to maintain it picked up, and also to cause it to be picked up when a train leaves the track section assuming of course that the front contact 21 of relay IR is closed.

I Let us assume that a train enters a track section and its wheels and axles constituting a good train-shunt are effective across the track rails in the usual manner. This train-shunt decreases the current in the track relay TR and also in the primary winding of the transformer TF. As ,soon as the current in the track relay TR falls below its drop away value, its contacts are released, but generally speaking this is rather slow due to the inductance of the relay and the fact that it has its windings shunted v by the train-shunt. The decrease in the current of the primary winding 4 of the transformer TF causes a transfer of energy to the secondary winding 5 and thus an impulse through the rectifier RE to the impulse relay IR. This relay IR usually responds very rapidly; and since the impulse relay IR is very sensitive, it picks up its contacts more quickly than the release of the track relay TR. For this reason, the back contact23 is opened and holds ,the signalsat stop and locks the switches or the like ',v e ry quickly upon the entrance of the train. I

Assuming that the train-shunt is effective in the usual manner found in good track circuits where the current in the track relay is maintained below the dropping away value of the track relay, the train passes through the track section and the relay IR remains deenergized and the track relay TR remains dropped away. But when the train leaves the track section, the train-shunt is removed rather abruptly, so that the relatively large current flowing from the track battery B through the limiting resistance LR is restored to a normal value. This increases the voltage across the track rails and results in an increase of current through the winding 4 and the track relay TR. The change of current in winding 4 is effective to cause an impulse to be supplied to the relay IR which picks up its front contact 21 and allows the application of the normal potential to the track relay TR which immediately picks up. The impulse received by the impulse relay IR is of suflicient duration as to allow the track relay TR to close its front contact 20 before the relay IR again releases, which of course occurs as soon as the current conditions have stabilized themselves to normal. 'Thus, a short interval after the train has left and normal conditions have restored, front contact 22 is closed as well as back contact 23 so that the switch and/or signal control circuits are restored to their normal conditions.

From the above description, it will be readily apparent that the presence of the transformer TF acts through the impulse relay IR to cause the pick up of the track relay TR when the. train leaves. Since this restoration is dependent upon the response of the impulse relay IR, the operability' of the transformer and rectifier. circuits is fully checked. Inlother words, if a failure should occur, the impulse relay IR would not respond and the track relay TR would not be picked up. This would hold any signals governed thereby at stop and would betray the fact of the failure Since the operation above described is the normal operation, the apparatus is'in a checked condition for taking care of abnormal train-shunt conditions.

For example, it may be that the train upon entrance to the track section will cause the release of the track relay and the actuation of the impulse relay as above described, but because of the sanding of the'rails for a braking operation or other extraneous matter found on the rails, the train-shunt may not remain fully effective. Under such "conditions, the train-shunt is actually intermittently effective to the extent that the interrail potential appearing across the relay end of the track section is intermittently varied. This causes a variation in the current through the primary winding 4 of the transformer TF which in turn causes impulses to be supplied to the impulse relay, IR causing it to be picked up- Thus, even though the variations or temporary losses of train-shunt might also cause the picking up of the track relay TR, the continued picking up of the relay IR opens back contact 23 and prevents anyoperation of the switch and/ or signal control circuits. As a matter of fact, it has been found in actual practice that a trainmoving' through a section where there is poor shuntingcharacteristics causes sufiicient variations in the track current that the impulse relay IR will pick up and remain picked up throughout such series of variations. Under suchcircumstances, with a conventional track circuit, the track relay would actually be picked up resulting in what is commonly known as a temporary loss of shunt but which would be a dangerous condition by permitting the switch and/or signal circuits to be released. In the present organization, the track relay TR cannot be picked of the track relay TR is wholly ineffective to' create a dangerous condition. In this way, the system of the present invention is protected against intermittently varyin'g train-shunt conditions; and a safe and reliable organiza- This form of the invention is very similar to the form shown in Fig. 2 in that all of the detecting apparatus is located at one end of the track section and thus adapts the organization to long track circuits.

More specifically, the track section is shown as having rails 2 separated from adjoining track sections by the usual insulated joints 3. At the right-hand end of the track section, a battery B and limiting resistor LR are connected in series across the track rails 2.

At the left-hand end of this track section, the transformer TF having primary winding 4 and secondary winding 5 is associated with the track relay TR and impulse relays IRN and IRX. The primary winding 4is connected directly across the track rails 2 in multiple with the track relay TR which is also connected across the track rails through the variable resistor 30, front contact 31 of relay TR and back contact 32 of relay IRN. Thus, the interrail potential at the relay end of this track section causes current to be supplied to the track relay TR and the winding 4 in multiple. The amount of current supplied to each is dependent upon their respective resistance values which are preferably about equal, but this is not a requirement for operability of the system.

The secondary winding 5 is connected through rectifier unit 33 to the entering impulse relay IRN. Also, the secondary winding 5 is connected to the exit impulse relay IRX through rectifier unit 34. These rectifier units 33 and 34 are so poled that the decay of flux in the transformer TF when a train enters the track section causes an impulse of a particular polarity which will flow through rectifier 33 and actuate the entering impulse relay IRN; but when the flux builds up in the transformer TF when a train leaves the track section the impulse supplied flows through recti fier unit 34 and the exit impulse relay IRX. These relays IRN and IRX are preferably polarized relays so as to be very sensitive. Their contacts are biased to positions shown so as to be responsive only to their respective polarities in the event of failure of the rectifier units 33 and 34. When these relays are thus made polar responsive structures, the rectifiers 33 and 34 serve mainly to direct the current pulses to one relay or the other. It should be understood that if desired the relays IRN and IRX may be placed in series and the rectifier units 33 and 34 omitted. The operation with this series arrangement of the relays remains exactly the same. Also, a single unitary relay structure distinctively responsive to polarity such as disclosed in the patent application by G. E. Marsh, Ser. No. 326,564 filed December 17, 1952, may be used if desired. In this prior application, it is described how the two armatures of the relay respectively respond to opposite polarities but are operated by the same core and winding structure.

The transformer TF may be of the closed magnetic circuit type which is usually the most efficient for the transfer of energy; but if it is desired to obtain impulses for the impulse relays which are higher in amplitude and shorter in duration, the transformer maybe made with an open type magnetic circuit.

When a train enters the track section providing a good train-shunt, the track relay TR is shunted and an impulse of energy is supplied to the relay IRN. This impulse relay IRN may, depending upon circumstances, open its back contact 32 before the track relay TR drops away to open its own front contact 31. If the external resistance 30 can be adjusted to a relatively high value, the track relay TR drops more quickly and may release about the same time that the back contact 32 opens. In any event, the entrance of a good train-shunt causes the release of the track relay TR, and since the front contact 31 is open, the track relay remains released regardless of a possible 10 momentary loss of shunt as the train passes through the section.

For example, if there is a momentary loss of trainshunt, the sudden rise and fall of current in the winding 4 of transformer TF causes an impulse of both polarities to be supplied thus causing the actuation of both the relays IRN and IRX. The actuation of the relay IRX closes front contact 35 which shunts out the stick contact 31, but the opening of back contact 32 of relay IRN under these circumstances prevents the track relay TR from picking up. Thus, not only is the track relay TR prevented from picking up holding its front contact 36 open, but the back contacts 37 and 38 of relays IRN and IRX are both open so that the switch and/ or signal control is assured of being maintained open during the presence of a train even though a momentary loss of shunt might occur.

When the train leaves the track section and the trainshunt effect is removed so that the normal interrail potential appears across the winding 4, an impulse of substantial value is supplied'to the relay IRX which responds closing front contact 35. This allows the track relay TR to pick up because this pulse is of such a polarity that the relay IRN does not respond and keeps back contact 32 closed. It should be noted here that the energy transferred through the transformer TF to the impulse relay IRX is of such a value to maintain it picked up for a sufiicient interval of time to allow the picking up of track relay TR and closing its front contact 31 before the front contact 35 again opens. In any event, the switch and/ or signal control is not closed through contacts 36, 37 and 38 until the track circuit conditions are stabilized.

From the above description it will be seen that the inductive pulse supplied upon the entrance of a train is used to actually open the circuit of the track relay, while the inductive pulse supplied upon the leaving of a train is used to pick up the track relay. In addition, the presence of variations in the effectiveness of the trainshunt causes the response of both relays IRN and IRX which maintains the track relay TR dropped away and the switch and/or signal controls opened.

Let us now assume that a relatively poor train-shunt is applied to the track section which is sufiiciently effective to cause a change in the current flowing through the winding 4 of transformer TF but is not sufficiently effective to reduce the current in the track relay TR below its drop away value. This change in the current in winding 4 causes an impulse to be applied to the entrance impulse relay IRN which responds by opening the back contacts 32 and 37. The opening of back contact 32 causes the track relay to drop away and it cannot again be picked up until the train leaves the section when an impulse of the proper polarity is supplied to the relay IRX.

If the train-shunt is relatively poor but is substantially constant, the track relay TR cannot be picked up because the relay IRX is dropped away with contact 35 open. If the relatively poor train-shunt varies in its effectiveness so as to cause the winding 5 to supply impulses to the relays IRN and IRX, both of these relays will be picked up so that the closure of contact 35 cannot allow the track relay TR to pick up because back contact 32 is open. In this way, the track relay TR is released upon the initial entrance of the train and is maintained released throughout the presence of that train even though it has only a relatively poor shunting effect. With this arrangement it is apparent that the response of the impulse devices is required in order to pick up the track relay and thus their operation is checked.

It should be understood in applying the principles of the present invention that various expedients may be used to facilitate the practice of the invention. For example, in Figs. 2 and 3 it may be desirable to connect the track relay directly across the track rails without any contacts, since the voltage and currents involved are very small and any variation in contact resistances might be undesirable.

-of relay CK, winding of relay CK, to

11 This feature has been. illustrated in the modification of Fig. 4. V

Fourth form (Fig. 4)

This form of the invention is very similar to the form shown in Fig. 3. All of the detecting apparatus is located at one end of the track section, and is arranged to provide etficient and sensitive operation particularly desired in long track circuits.

Since this form is substantially the same as the form of Fig. 3, all of the general operating characteristics are applicable and will not be repeated in detail; but particular emphasis will be placed upon the structural differences illustrated in this Fig. 4.

More particularly, the track relay TR and its variable resistor 40 is connected directly across the track rails 2 in multiple with the primary winding 4 of the impulse transformer TF. This makes it so that there are no contacts in the track relay connection, which not only eliminates the contact variables from the circuit but also simplifies the wiring problems.

The relays IRN and IRX, which are polar relays as described in connection with Fig. 3, have been shown in series instead of in multiple. These relays respond to current flow in the direction of their respective arrows. This arrangement removes the need for rectifier units and increases the reliablility of the check on the impulse responsive apparatus.

A checking relay CK is normally energized through a circuit from and including front contact 41 of track relay TR, back contact 42 of relay IRN, front contact 43 This stick circuit normally maintains the check relay CK picked up so that its front contact 44 is maintained steadily closed. This provides that the switch and/ or signal control circuits are unlocked and may be used in the usual ways when the track section is unoccupied.

The entrance of a train drops the check relay CK both because the track relay TR is shunted opening front contact 41, and because the impulse responsive relay IRN picks up in response to the reduction of current in the primary winding 4 of transformer TF. Such release of the check relay CK opens contact 44 preventing any subsequent operation of the track switch and controls to stop any signals governing traflic thereover.

When the train leaves the track section, the rapid increase of current in the primary winding 4 of transformer TF due to the restoration of the normal interrail potential, causes an inductive impulse to be supplied to the impulse relays. It is on such a polarity that the polar relay IRX is picked up closing front contact 45 to complete a pick-up circuit for the check relay CK from through a circuit including front contact 41 of track relay TR, back contact 42 of relay IRN, front contact 45 of relay IRX, windings of relay IRX, to Since front contact 41 and back contact 42 are closed under this condition, the closure of front contact 43 upon the relay CK picking up, completes the stick circuit so that the subsequent release of the relay IRX at the termination of exit impulse still maintains the check relay CK energized. This, of course, closes contact 44 and releases the switch and/or signal control circuits for operation.

It will be observed that not only are the exit and entrance impulses effective to control the relay CK, but also variations in interrail potential during the passage of a car or train having a relatively poor train-shunt actuates both the impulse responsive relays; particularly, the relay vIRN which opens back contact 42 and maintains the check relay CK deenergized.

As above mentioned, the general operating characteristics of this form of the invention are the same as described in connection with Fig. 3 and will not be further discussed.

It should be noted, however, that this form of the invention requires only -.a single contact on each of the detecting relays TR, IRX and IRN. This makes it so- 12 that these relays may be made very sensitive. The repeating check relay CK may have as many front and back contacts as required forv the application of switch and signal controls, since its operation is from a local source of energy.

Having described several forms of track circuits responsive to variations in train-shunt values as specific embodiments of the present invention, it is desired to be understood that these forms are selected to facilitate in the disclosure of the invention rather than to limit the number of forms which it may assume; and it is to be further understood that various modifications, adaptations What I claim is: 1. In combination with a section of railroad track insulated from adjoining sections, a source of energy, a

limiting resistor, and an impulse transformer having primary and secondary windings, circuit means connecting said primary winding and said source of energy and said limiting resistor in series across the rails at one end of said section, rectifier circuit means, an impulse responsive relay circuit means connecting said secondary winding through said rectifier circuit means to said impulse responsive relay, a track relay connected across the rails at the other end of said section through its own front contact, circuit means including a front contact of said impulse relay for at times shunting said front contact of said track relay, and circuit means controlled through a front contact of said track relay in series with a back contact of said impulse responsive relay.

2. In combination with a section of railroad track insulated from adjoining sections, a source of energy connected across the rails at one end of said section, a track relay connected across the rails at the other end of said section through its own front contact, electromagnetic means responsive only to variations in current flow in said track circuit to provide a distinctive control only when there are such variations, circuit means governed by said electromagnetic means to render said track relay responsive to said variation in current flow whenever said electromagnetic means indicates variations in current flow and for a limited time thereafter, said circuit means requiring the response and said distinctive control of said electromagnetic means each time a train leaves the track circuit after having caused said track relay to be released before said track relay can be picked up, and signaling apparatus requiring the restoration of said track relay and said electromagnetic means to the normal position before clearing.

3. In combination with a section of railroad track insulated from adjoining track sections, a source of energy connected in series with a limiting resistor across the rails at one end of said section, a track relay connected across the rails at the other end of said section so as to be responsive to the interrail potential, said track relay connection including its own front contact to constitute a stick circuit organization, electromagnetic means responsive only to variations in current flow in said track circuit and including a sensitive relay, circuit means controlled by said sensitive relay in its picked up condition for allowing said track relay to respond to the interrail potential independently of the open condition of said front contact of said track relay, and trafiic controlling circuit means controlled jointly by said track relay and said sensitive relay.

4. In combination with a section of railway track insulated from adjoining sections, a source of energy and a limiting resistor connected in series across the rails at one end of said section, a track relay connected across the rails at the other end of said section in series with its own front contact to comprise a stick circuit organization, electromagnetic means responsive only to variations of current flow in said track circuit and including a senmeans for governing switch and/or signal controls in cluding a front contact of said track relay and a back contact of said sensitive relay;

5. In combination with a section of railway track insulated from adjoining sections by suitable insulated joints, a source of energy and'a limiting resistor connected in series across the rails at one end of-saidsection, a track relay, an impulse transformer having primary and secondary windings and polarity responsive relay means at the other end of said section, circuit means connecting the primary winding of said impulse-transformer acrossthe rails of said section at that end, circuit means connecting said track relay through its own front contact and a contact of said polarity responsiverelay means across the rails of said section in multiple with said primary winding, circuit means connecting the secondary winding of said transformer to said polarity responsive relay means with connections such that an impulse of a polarity caused upon the shunting of said track rails opens said'contact in said circuit for said track relay and an impulse of the opposite polarity does not do so but actuates anothercontact, circuit means including said another contact for at times shunting said front contact of said track relay, and switch and/ or signal control means controlled by a front contact of'said track, relay and'back' contacts of said polarity responsive relay means.

6. In combination with a section of railroad track insulated from adjoining sections, a source of direct current energy and a limiting resistor connected across the track rails at one end of the section, a track relay directly connected across the track rails of the other end of said section, impulse responsive means associated with said track relay and said track rails so as to provide pulses of distinctive polarity respectively when said section becomes occupied and unoccupied, a check relay having pick-up and stick circuits, polarized relay means associated with said impulse responsive means to be distinctively responsive to said impulses of different polarities, a pick-up circuit for said check relay including a front contact of said track relay and a contact closed only when said impulse responsive means provide said polarized relay means with a pulse characteristic of the section becoming unoccupied, and stick circuit means for said check relay including a front contact of said track relay and a contact of said polarized relay means closed only when supplied with a pulse by said impulse responsive means of a polarity characteristic of a train entering said track section and also a front contact of said check relay, and signaling control circuits controlled by contacts of said check relay.

7. In combination with a section of railroad track insulated from adjoining sections, a source of direct current energy and a limiting resistor connected across the track rails at one end of the section, a track relay and an impulse responsive means associated with the other end of said section, said track relay being directly connected across the track rails of said section, a check relay having pick-up and stick circuits, and circuit means including contacts of said impulse responsive means and a contact of said track relay for deenergizing said pick-up and stick circuits when a train enters said track section and for energizing said pick-up circuit only when a train leaves said section and it is wholly unoccupied.

8. In combination with a section of railroad track insulated from adjoining sections, a source of direct current energy and a resistor connected across the track rails at one end of the section, a track relay connected across the track rails at the other end of said section and normally actuated by the interrail potential supplied by said source but released by the presence of an effective train-shunt, impulse responsive means associatedlwith said:

section andLac-tuated in response to the entrance of a train into the-section andto the exit of atrain from the: section, said impulse responsive means, also bei'ng-actu ated in response to variations in the value of-interrail potential during the passage of the train through the section, said actuation of said impulse responsive meansbeing dependent of the actuation of said trackrelay, and signaling means controlled to the same condition by the release of said track relay and also by'theactuation of said impulse responsive means alone.

9. In combination with a section of railroad track insulated from adjoining sections, a source of direct current energy and a resistor connected across the track rails at one end of'the section, a track relay connected across the track rails at'the other end of said section and normally actuated by the interrail potentialsupplied by said source but released by the presence of a train-shunt, impulse responsive means associated with said section and actuated in response to the entrance of atrain into the section and the exit of a train from the section, said impulse responsive means also being actuated in-response to variations in the value of interrail potential during the passage of the train through the section, and signaling means controlled jointly by said track relay and saidimpulseresponsive means to the same condition regardless of whether said track relay is released'by the'presence of a train in said track section or whether said impulse responsive means is actuated in response to the presence of such train in the section, and circuit means associated With-said track relay and said impulse responsive means for checking the response of said impulse responsive meanseach time a train leaves said section with said track relay released.

10. In a direct current track circuit, a source of energy at one end and a track relay at the other end, electromagnetic means responsive to variations in the interrail potential due to the passage of a train over the track circuit to give a distinctive control, signaling circuits controlled jointly by said track relay and by the distinctive control of said electromagnetic means, and circuit means requiring the response and said distinctive control of said electromagnetic means each time a train leaves the track circuit after having caused said track relay to be released before said signaling circuits can be restored to normal conditions.

11. In a track circuit organization for railroads, a section of track having its rails insulated from adjoining sections, a source of energy, a limiting resistor, circuit means connecting said source and said limiting resistor in series across the rails at one end of said section, occupancy detecting means including a track relay initially actuated by a train-shunt to manifest the occupied condition of said section and remaining in its actuated condition until restored, and restoring means for said occupancy detecting means including an impulse responsive relay caused to be actuated in response to current changes in the track circuit due to the variations of a train-shunt, said restoring means being efiective for a limited time only to act upon said occupancy detecting means for actuating it to its normal condition, and a control circuit means including a contact of said occupancy detecting means and a contact of said impulse responsive relay, whereby the failure of said restoring means is betrayed by the failure of said control circuit means to have its circuit closed by said occupancy detecting means.

12. In combination with a section of railroad track insulated from adjoining sections, a source of direct current at one end of said track section being connected to the rails of said track section, a track relay at the other end of said track section being energized by the interrail potential when said track section is unoccupied but becoming deenergized when said track section is occupied by a vehicle providing an effective interrail shunt, inductive circuit means associated with said track section and being actuated to a distinctive condition by abrupt variations in said interrail potential occurring when said track section becomes either occupied or unoccupied and also by said abrupt variations of said interrail potential occurring when said track section is occupied by a vehicle providing an intermittently efiective interrail shunt, and signaling means controlled jointly by said track relay and said inductive circuit means to the same condition regardless of whether said track relay is released by the presence of a train in said track section or whether said inductive circuit means is actuated to its distinctive condition in response to the presence of said vehicle in said track section.

13. In combination with a section of railroad track insulated from adjoining sections, a source of direct current energy and a resistor connected across the track rails at one end of the section, a track relay at the other end of said track section, said track relay being normally actuated-by the interrail potential when the track section is unoccupied and released when said track section is occupied by a train having an effective interrail shunt, impulse responsive means including a sensitive relay associated with said track relay actuated by the interrail potential variations due to sudden occupancy or lack of occupancy of said track section and further actuated by any variations in interrail potential during occupancy of said track section caused by said interrail shunt becoming intermittently inefiective, a control circuit governed by said track relay and said impulse responsive means, circuit means for checking the proper operations of said impulse responsive means including said sensitive relay, said circuit means including a stick circuit for said track relay and a pickup circuit for said track relay including a contact closed only upon the actuation of said sensitive relay, whereby said track relay when once released requires the response of said sensitive relay in order to be picked up. I

14. In a signaling organization for railways, a section of track having its ends insulated from the adjoining sections, a source of energy connected in series with a limiting resistor'across the rails at one end of the section, occupancy detecting means including a track relay connected across said rails at the other end of said section and released by each efiective train shunt, electromagnetic means connected to said track rails and including a sensitive relay independently operative in response to variations in interrail potential occurring during occupaney of said section of track, a control circuit controlled by operation of said track relay due to the detection of an effective train shunt, said control circuit also being controlled by each operation of said sensitive relay, and check circuit means for checking proper operation of said sensitive relay in response to interrail potential variations and including a stick circuit organization having pick up circuit required to be closed by the operation of said sensitive relay following the detection of a train shunt by said track relay before said control circuit can be restored to a normal condition.

References Cited in the file of this patent UNITED STATES PATENTS 2,040,969 Abernethy May 19, 1936 2,053,897 Crago Sept. 8, 1936 2,218,125 Sosinski Oct. 15, 1940 

